1. Field of the Invention
This invention relates to an ink-jet ink, a method for decreasing kogation on the surface of a heater for heat application to the ink, a method for ink-jet recording, an ink-jet recording apparatus, a recording unit, and a method for increasing life of the ink-jet recording head.
2. Related Background Art
There have been proposed various types of ink-jet recording methods. According to one ink-jet recording method, the so-called bubble-jet recording method described in, for example, Japanese Patent Application Laid-Open No. 54-51837, ink is ejected in the form of ink droplets by the action of thermal energy. This ink-jet method has a feature that high quality images can be formed on plain paper having no special coating layer at high speed and at low cost, due to the very simple structure of the high-density multinozzles. In this method, rapid heating of the heater in the recording head induce bubble generation in the liquid on the heater with rapid bubble volume inflation, and the action force due to this rapid volume increment ejects a liquid droplet from the nozzles arranged at the tip of the recording head to make the droplet fly to the recording material and attach thereon. Printing is thus carried out.
In this method, however, the heater in the recording head is repeatedly heated to eject ink during mass printing. This may cause the deposition of the decomposition product of the ink, so-called koga (scorch), on the surface of the heater. Deposition of koga prevents the efficient transmission of the thermal energy from the heater to the ink, resulting in the decrease in the volume and speed of the ejected droplets in comparison with the initial stage, which affects the image quality. In such a case, the recording head must be changed with a new one in order to continuously achieve high quality printing. To the users, this means a higher printing cost in total.
Thus, further reduction of kogation on the heater in order to prolong the recording head life has been one of the important technical problems to be improved in the art of bubble-jet method. There has been proposed, for example, ink containing an oxoanion (Japanese Patent Application Laid-Open No. 3-160070), where as an oxoanion, described are phosphate salts, polyphosphates, phosphate esters, arsenates, molybdates, sulfates, sulfites and oxalates.
However, when the ejection of such an ink is repeated, the oxoanions in the ink dissolve the outermost protection layer of the heater, which layer is comprised of a metal or a metal oxide or both such as tantalum. In addition, such an ink is still insufficient in kogation prevention.
An object of the present invention is to provide a method for decreasing kogation on the surface of the heater which is used for applying thermal energy to the ink in a recording head so as to eject the above ink from the recording head.
Another object of the present invention is to provide an ink-jet recording apparatus which enables high quality printing and prolonged product life of the recording head.
A further object of the present invention is to provide a recording unit which enables high quality printing over a prolonged period.
Still another object of the present invention is to provide a method for prolonging the product life of the recording head to lower the cost in high quality printing.
According to one aspect of the present invention, an ink for ink-jet recording comprises:
(a) a coloring material,
(b) a liquid medium, and
(c) an ammonium salt of an acid having a methyl or methylene group and a carboxylic group.
According to another aspect of the present invention, an ink for ink-jet recording comprises:
(a) a coloring material,
(b) a liquid medium, and
(c) an ammonium aldonate.
According to still another aspect of the present invention, an ink for ink jet recording comprises:
(a) a coloring material,
(b) a liquid medium, and
(c) at least one or more compounds selected from the group consisting of monoammonium citrate, diammonium citrate, and triammonium citrate.
According to still another aspect of the present invention, a method alleviates kogation on a surface of a heater of a recording head of an ink-jet printer, the heater being arranged to apply thermal energy to an ink in the recording head to eject the ink from an orifice in the recording head, wherein the heater has an outermost protection layer containing at least one of a metal and a metal oxide, and the ink is one of the above-mentioned inks.
According to further aspects of the present invention, an ink-jet recording method and an ink-jet recording apparatus are provided in which the ink used therein is one of the above-mentioned inks.
When one of the above-mentioned inks is used in an ink jet recording apparatus where ink is ejected as an ink droplet by the action of thermal energy applied from the heater, kogation on the outermost surface of the heater is very effectively reduced. The mechanism of the kogation alleviation is unclear, but it is considered that the component (c) of the ink of the invention interacts with the metal and/or the metal oxide constituting the outermost protection layer of the heater to prevent koga deposition or to enhance the decomposition of koga or peeling off of koga from the surface.
Further studies of the inventors have revealed that the effect of the ink of the invention becomes more eminent when the metal and/or metal oxide contained in the protecting layer of the heater is tantalum or tantalum oxide. Further the energy amount applied to the heater can be controlled in relation to the minimal energy required for ink ejection to improve the kogation alleviation effect of the present invention without disconnection of the heater with excellent ejection durability.